Slat expander roll



July 10,v 1962 R. D. FOLEY sLAT EXPANDER ROLL Filed May 8, 196].

INVENTOR. R /c/ 0rd D. F 0 /ey ,www/w ENT' United States Patent3,042,989 SLAT EXPANDER RGLL Richard D. Foley, Bay City, Mich., assignerto The Dow Chemical Company, Midland, Mich., a corporation of Delaware.

Filed May 8, 1961, Ser. No. 108,592 Claims. (Cl. 26--64) This inventionrelates to a method and apparatus for the handling of smooththermoplastic resinous film. lt more particularly relates to an improvedexpander roll for the handling of such webs, in coating machinery,slitting equipment and the like.

Advantageously, a wrinkle free web is obtained by passing the web over aroll having a plurality of movable slats or bars on itsV surface and soconstructed and arranged that each slat is divided into at least threeportions, a centrally positioned fixed portion and 2 portions which moveoutwardly at least on part of the rotating cycle. Such a roll isdescribed in United States Letters Patent 2,969,578. When a slatexpander roll is employed to handle smooth thermoplastic webs such aslfilms prepared from polystyrene, polyethylene and saran and the like,there is a marked tendency for the web to wander to one side or theother of the roll and adequate tracking is not maintained unless underconstant manual or automatic control. Such a condition is generallyunsatisfactory and results in considerable expense as well as unnecesarycomplicated equipment.

It is an object of this invention to provide an improved slat expanderroll for the handling of thermoplastic webs.

It is a further object of this invention to provide an improved surfaceconfiguration for a slat expander roll.

It is yet another object of this invention to provide a slat expanderroll which will cause improved tracking of thermoplastic Webs.

These benefits and other advantages are obtained by providing in a slatexpander roll for a web comprising a plurality of slats peripherallydisposed about and parallel to the axis of said roll, each of said slatscomprised of at least a centrally disposed fixed portion and movableportions disposed at opposite ends of said fixed portion, said movableportions adapted to move toward and away from said central fixed portionas said roll is rotated, said motion Ibeing in a direction generallyparallel to the axis of rotation, the improvement which comprises saidcentral fixed portion of each said slat having a roughened surface, andsaid movable portions of each of said slats having an exposed less roughsurface than said roughened surface, the difference in roughness beingsucient to maintain tracking of said Web on said roll.

Further features and advantages of the invention will become moreapparent in view of the following specification and drawing wherein:

The FIGURE schematically depicts the handling of a web in accordancewith the invention. A pivotally mounted supply roll provides a supply oftransparent thermoplastic web 11 to a slat expander roll generallyindicated by the reference numeral 13. The pivotally mounted slatexpander roll 13 has peripherally affixed thereto a plurality of slats15. Each slat 15 is comprised of a fixed central portion 16 and movableend portions 17 and 18. The fixed central portion 16 is provided with aroughe'ned surface 20, whereas the slat portions 17' and 18 havesmoother surfaces 2.1 and 22. The slat portions 17 and 18 are caused tomove away from the central portion 16 while in contact with film 11 by acam mechanism within the roll (not shown).

In operation a roll in accordance with the invention, is often employedimmediately after unwinding from a supply roll such as is illustrated inFIGURE l intermediice ate another operation performed on the web, forexample, in feeding a coating apparatus or a printing press.Advantageously, where the web is to be processed through a variety ofoperations it is often advantageous to incorporate a slat expander rollin accordance with the invention at any stage or location where there isa tendency for the generation of wrinkles in the web or tendency togenerate wrinkles through curling, shrinkling or stretching. Rolls inaccordance with the invention may be installed as idler rolls, that is,being driven by the friction of the web passing thereover or ultimatelythe roll may be driven to provide tension and a forwarding actionthereon.

The surface 2f) of the fixed central portion 16 of each slat inaccordance with the invention rnust be rougher than the correspondingsurfaces Z1 and 22' of the movable slat portions 17 and 18. The precisedegree of roughness required will depend upon the particular materialbeing handled. An extremely rough surface 20 on the central portion 16would tend to perforate or mark the web being handled whereas if it isexcessively smooth the beneficial effects will be lost. With anexcessively smooth surface 20 on the central portion 16 when compared tothe finish of the surfaces 21 and 22 proper tracking will not beobtained. Advantageously, for many thermoplastic Webs a finish on thesurface 20 advantageously is between about 20 and about 700 microinchesas defined in American Standard ASA B46.2l952, whereas the outer movablesurfaces 21 and 22 advantageously are provided with a surface finishhaving a roughness up to about 300 microinches. Generally the finish inmicroinches of the central portion 20 should be about twice thenumerical value of the finish in microinches of the movable surfaces 21and 22. However, beneficially no lower limit usually exists for thefinish of the movable surfaces 2'1 and 2.2 although in cases wherehandling certain thermoplastic webs which tend to have a slightly oilysurface such as certain of the saran and vinyl chloride polymercompositions it is often beneficial to employ a finish no smoother thanabout 5 microinches` By way of further illustration, a roll inaccordance with the invention was prepared which had a closed length,that is, with the movable slats in their closest relationship to thefixed central portion, of l7 inches. The roll had a diameter of 6 inchesand ten three-piece slats extended the entire length thereof. The slatsdisposed about the circumference were equally spaced about the peripheryof the roll. The central portion of the slats were sandblasted to afinish of about 60 microinches and the movable portions of the slats hada roughness of about 20 microinches. These finishes were determined bycomparison with a sample finish specimen as specified in AmericanStandard ASA B46.21952. This roll was incorporated into a coatingapparatus and employed to smooth a web of oriented polystyrene filmabout l mil in thickness coming from a supply roll. After several monthsof operation, no tendency was observed for the web to wrinkle or towander to either side of the roll. By Way of contrast, a similar rollhaving a uniform finish of about 50 microinches on the surface of thefixed and movable slat portions in the same equipment required theconstant attention of an operator to maintain tracking and manuallycorrect severe wrinkling.

Substantially similar beneficial results are achieved when a roll inaccordance with the invention is employed with other thermoplastic webssuch as polyethylene, polypropylene, polyvinyl chloride, saran,polyester film such as mylar and the like.

The apparatus of the invention may be embodied with various alterationsand modifications which may differ particularly from those that havebeen described in the preceding specification and description. For thisreason, it is to be fully understood that all of the foregoing isintended to be merely illustrative and is not to be construed orinterpreted as being restrictive or otherwise limiting of the presentinvention, excepting as it is set forth and defined in the heretoappended claims.

What is claimed is:

1. In a slat expander roll for a web comprising a plurality of slatsperipherally disposed about and parallel to the axis of said roll, eachof said slats comprised of at least a centrally disposed ixed portionand movable portions disposed at opposite ends of said fixed portion,said movable portions adapted to move toward and away from said centralxed portion as saidI roll is rotated; said movement being in a directiongenerally parallel to the axis of rotation, the improvement whichcomprises providing said central fixed portion of each said slat with anexposed roughened surface, and said movable portions of each of saidslats with an exposed less-rough surface, the difference in roughnessbeing sufficient to maintain tracking of said web.

. 2. The roll of claim 1, wherein said central iixed portion is providedwith an exposed surface having a surface roughness having a value atleast twice the numerical value of the roughness of said less roughsurface.

3. The roll of claim 2, wherein the exposed surface of said centralportion has a surface roughness between about 2O and 700 microinches.

4. The roll of claim 3, wherein each of said slats are composed of onecentral xed portion and two movable portions.

5. The roll of claim 4, wherein each said xed portion has a surfaceroughness of about 6() microinches and said movable portions a surfaceroughness of about 20 micro inches.

References Cited in the tile of this patent UNITED STATES PATENTSWheeler Sept. 28, 1926 King May 12, 1953 Lembo Ian. 31,1961

